Zhang Zhiliang huddled with his family on Sunday in the stairwell of a Beijing hotel, confounded by how little was known about the disappearance of Malaysia Airlines flight 370, which carried his 26-year-old cousin and 238 others.

"I don't understand," Mr. Zhang said over the sobs of relatives. "We have all the technology in the world these days, and how is it that we can't locate them? GPS, phones, everything is so...